Method for producing silica particle, method for producing silica sol, polishing method, method for producing semiconductor wafer and method for producing semiconductor device

Abstract

To provide a method for producing silica particles that resist secondary aggregation, have excellent dispersion stability, and are suitable for polishing, a method for producing a silica sol containing the silica particles obtained by the production method, a polishing method suitable for polishing, a method for producing a semiconductor wafer, including the polishing method, and a method for producing a semiconductor device, including the polishing method.SOLUTION: A method for producing silica particles includes step (1) of adding, into a solution (A) containing an alkali catalyst, a solution (B) containing tetraalkoxysilane and a solution (C) containing an alkali catalyst, and subjecting the tetraalkoxysilane to hydrolysis and condensation reactions.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing silica particles, a method for producing silica sol, a polishing method, a method for producing semiconductor wafers, and a method for producing semiconductor devices. [Background technology]

[0002] Polishing methods using polishing solutions are known as methods for polishing the surfaces of materials such as metals and inorganic compounds. In particular, in the final polishing of prime silicon wafers for semiconductors and reclaimed silicon wafers, as well as chemical mechanical polishing (CMP) for planarizing interlayer insulating films during semiconductor device manufacturing, forming metal plugs, and forming buried wiring, the surface condition significantly affects the semiconductor characteristics. Therefore, the surfaces and edge faces of these components must be polished with extremely high precision.

[0003] In such precision polishing, polishing compositions containing silica particles are employed, and colloidal silica is widely used as the abrasive grains that are the main component thereof. Colloidal silica is known to be produced by different methods, such as by thermal decomposition of silicon tetrachloride (fumed silica, etc.), by deionization of alkali silicate such as water glass, and by hydrolysis and condensation reaction of alkoxysilane (generally referred to as the "sol-gel method").

[0004] Many studies have been conducted on methods for producing silica particles. For example, Patent Documents 1 to 4 and Non-Patent Documents 1 and 2 disclose methods for producing silica particles by hydrolysis and condensation reactions of alkoxysilanes. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 11-60232 [Patent Document 2] Japanese Patent Application Publication No. 4-187512 [Patent Document 3] International Publication No. 2013 / 073025 [Patent Document 4] Japanese Patent Application Publication No. 61-209910 [Non-patent literature]

[0006] [Non-Patent Document 1] "Technology and Properties of High-Purity Colloidal Silica," Shinichi Sugita, JETI, Vol. 61, No. 3, pp. 58-61, (2013). [Non-patent document 2] "Controlled growth of monodisperse silica spheres in the micron size range" Stäber, Journal of Colloid and Interface Science, Vol. 26, No. 62-69, (1968). Summary of the Invention [Problem to be solved by the invention]

[0007] Generally, as disclosed in Non-Patent Document 1, silica particles in silica sol obtained by the hydrolysis and condensation reaction of alkoxysilanes exhibit various shapes such as spherical, cocoon-like, and irregular shapes immediately after synthesis.

[0008] Patent Document 1 discloses cocoon-shaped silica particles, and Patent Document 2 discloses irregularly shaped (elongated) silica particles. However, when cocoon-shaped or irregularly shaped silica particles such as those disclosed in Patent Documents 1 and 2 are used as polishing compositions, while the polishing compositions have excellent polishing power, they tend to scratch the object to be polished, making it difficult to obtain an object to be polished with a smooth surface. Furthermore, when cocoon-shaped or irregularly shaped silica particles are used as polishing compositions, the silica particles are prone to change in physical properties, such as secondary aggregation, during storage or use, resulting in poor polishing performance stability. To solve these problems, more spherical silica particles are required.

[0009] When silica particles having a large particle size are used in a polishing composition, although they have excellent polishing power, they tend to scratch the object to be polished, making it difficult to obtain an object with a smooth surface.Furthermore, the silica particles are prone to change in physical properties during storage or use, such as secondary aggregation or sedimentation, resulting in poor polishing performance stability. To solve these problems, silica particles with smaller particle sizes are required.

[0010] Patent Documents 3 and 4 and Non-Patent Document 2 disclose silica particles that are nearly spherical and have a small particle size, but do not disclose silica particles that are nearly spherical and have a small particle size, and therefore cannot be said to be sufficient to solve the above-mentioned problems of not being able to obtain a polished object with a smooth surface and of poor stability of polishing performance.

[0011] The present invention has been made in view of these problems, and an object of the present invention is to provide a method for producing silica particles that suppress secondary aggregation, have excellent dispersion stability, and are suitable for polishing, and a method for producing a silica sol containing the silica particles obtained by the production method. Another object of the present invention is to provide a polishing method suitable for polishing, a method for producing a semiconductor wafer including the polishing method, and a method for producing a semiconductor device including the polishing method. [Means for solving the problem]

[0012] Conventional silica particles, particularly non-spherical silica particles such as cocoon-shaped or irregularly shaped silica particles or silica particles with large particle diameters, have the problem that when used as a polishing composition, a polished object with a smooth surface cannot be obtained and the polishing performance is poor in stability. However, as a result of intensive research, the present inventors have found that by optimizing the method of adding the solution during the hydrolysis reaction and condensation reaction of tetraalkoxysilane, silica particles with a large circularity coefficient and a small particle diameter can be obtained, and have completed the present invention.

[0013] That is, the gist of the present invention is as follows. [1] A method for producing silica particles, comprising the following step (1): Step (1): A step of adding a solution (B) containing a tetraalkoxysilane and a solution (C) containing an alkali catalyst to a solution (A) containing an alkali catalyst, and causing the tetraalkoxysilane to undergo a hydrolysis reaction and a condensation reaction. [2] The method for producing silica particles according to [1], wherein the alkali catalyst in the solution (A) is ammonia. [3] The method for producing silica particles according to [1] or [2], wherein the alkali catalyst in the solution (C) is ammonia. [4] The method for producing silica particles according to any one of [1] to [3], wherein the reaction temperatures of the hydrolysis reaction and the condensation reaction are 40° C. or higher. [5] The method for producing silica particles according to any one of [1] to [4], wherein the average Heywood diameter of the silica particles measured by a field emission scanning electron microscope is 20 nm or less. [6] The method for producing silica particles according to any one of [1] to [5], further comprising the following step (2): Step (2): Concentrating the dispersion of silica particles obtained in step (1) and adding a dispersion medium [7] The method for producing silica particles according to [6], further comprising the following step (3): Step (3): A step of subjecting the dispersion of silica particles obtained in step (2) to a pressure and heat treatment. [8] A method for producing silica sol, comprising the method for producing silica particles according to any one of [1] to [7]. [9] The method for producing a silica sol according to [8], wherein the concentration of silica particles in the silica sol is 10% by mass to 25% by mass.

[10] A polishing method, comprising polishing using a polishing composition containing the silica sol obtained by the method for producing a silica sol according to [8] or [9].

[11] A method for manufacturing a semiconductor wafer, comprising the polishing method according to

[10] .

[12] A method for manufacturing a semiconductor device, comprising the polishing method according to

[10] . [Effects of the Invention]

[0014] The method for producing silica particles of the present invention can obtain silica particles with a large circularity coefficient and a small particle diameter, and the obtained silica particles suppress secondary aggregation and have excellent dispersion stability, and when used as a polishing composition, a polished object with a smooth surface can be obtained and the polishing performance is excellent in stability.Furthermore, the method for producing silica sol of the present invention can be used as a polishing composition, and a polished object with a smooth surface can be obtained and the polishing performance is excellent in stability. The polishing method of the present invention is suitable for polishing. Furthermore, the method for producing a semiconductor wafer and a method for producing a semiconductor device of the present invention include the polishing method of the present invention, and therefore have excellent production stability for the object to be polished. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention will be described in detail below, but the present invention is not limited to the following embodiments and can be practiced with various modifications within the scope of the gist. In this specification, when the expression "to" is used, it is used as an expression including the numerical values ​​or physical property values ​​before and after it.

[0016] (Method of producing silica particles) The method for producing silica particles of the present invention includes the following step (1). Step (1): A step of adding a solution (B) containing a tetraalkoxysilane and a solution (C) containing an alkali catalyst to a solution (A) containing an alkali catalyst, and causing the tetraalkoxysilane to undergo a hydrolysis reaction and a condensation reaction.

[0017] Step (1) is a step in which a solution (B) containing a tetraalkoxysilane and a solution (C) containing an alkali catalyst are added to a solution (A) containing an alkali catalyst, and the tetraalkoxysilane is subjected to a hydrolysis reaction and a condensation reaction.

[0018] The solution (A) preferably contains water, since this allows the hydrolysis reaction and condensation reaction of the tetraalkoxysilane to proceed.

[0019] The solution (A) preferably contains a solvent other than water, since this provides excellent dispersibility of the tetraalkoxysilane in the reaction solution. Examples of solvents other than water in solution (A) include methanol, ethanol, propanol, isopropanol, and ethylene glycol. These solvents may be used alone or in combination of two or more. Among these solvents, alcohol is preferred, more preferably methanol or ethanol, and even more preferably methanol, because it easily dissolves tetraalkoxysilane, the by-products used in the hydrolysis reaction and the condensation reaction are the same as those used in the hydrolysis reaction and the condensation reaction, and it is convenient for production.

[0020] The solution (A) contains an alkali catalyst. Examples of alkali catalysts in solution (A) include ethylenediamine, diethylenetriamine, triethylenetetraamine, ammonia, urea, ethanolamine, and tetramethylammonium hydroxide. These alkali catalysts may be used alone or in combination of two or more. Among these alkali catalysts, ammonia is preferred because it has excellent catalytic activity, is easy to control particle shape, can suppress the inclusion of metal impurities, is highly volatile, and is easily removable after the hydrolysis reaction and the condensation reaction.

[0021] The concentration of water in solution (A) is preferably 3% by mass to 30% by mass, and more preferably 5% by mass to 25% by mass, based on 100% by mass of solution (A). When the concentration of water in solution (A) is 3% by mass or more, the hydrolysis reaction rate of tetraalkoxysilane is easily controlled. Furthermore, when the concentration of water in solution (A) is 30% by mass or less, the reaction balance between the hydrolysis reaction and the condensation reaction is good, and the particle shape is easily controlled.

[0022] The concentration of the alkali catalyst in solution (A) is preferably 0.5% by mass to 2.0% by mass, and more preferably 0.6% by mass to 1.5% by mass, based on 100% by mass of solution (A). When the concentration of the alkali catalyst in solution (A) is 0.5% by mass or more, aggregation of silica particles is suppressed, and the dispersion stability of silica particles in the dispersion is excellent. Furthermore, when the concentration of the alkali catalyst in solution (A) is 2.0% by mass or less, the reaction does not proceed excessively quickly, and the reaction controllability is excellent.

[0023] The concentration of the solvent other than water in the solution (A) is preferably the balance of water and the alkali catalyst.

[0024] The solution (B) contains a tetraalkoxysilane. Examples of tetraalkoxysilanes in solution (B) include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetraisopropoxysilane. These tetraalkoxysilanes may be used alone or in combination of two or more. Among these tetraalkoxysilanes, tetramethoxysilane and tetraethoxysilane are preferred, with tetramethoxysilane being more preferred, because they undergo a rapid hydrolysis reaction, are less likely to leave unreacted substances, are highly productive, and allow stable silica sol to be easily obtained.

[0025] The raw materials for the silica particles may be raw materials other than tetraalkoxysilane, such as low condensates of tetraalkoxysilane. However, due to their excellent reactivity, it is preferable that, out of 100% by mass of all raw materials constituting the silica particles, tetraalkoxysilane accounts for 50% by mass or more and raw materials other than tetraalkoxysilane accounts for 50% by mass or less, and it is more preferable that tetraalkoxysilane accounts for 90% by mass or more and raw materials other than tetraalkoxysilane accounts for 10% by mass or less.

[0026] The solution (B) may contain only tetraalkoxysilane without containing a solvent, but it is preferable that the solution (B) contains a solvent, as this improves the dispersibility of the tetraalkoxysilane in the reaction liquid. Examples of the solvent in solution (B) include methanol, ethanol, propanol, isopropanol, and ethylene glycol. These solvents may be used alone or in combination of two or more. Among these solvents, alcohol is preferred, more preferably methanol or ethanol, and even more preferably methanol, because the solvents used in the hydrolysis reaction and the condensation reaction and the by-products are the same, and therefore the production is easy.

[0027] The concentration of the tetraalkoxysilane in solution (B) is preferably 60% by mass to 95% by mass, and more preferably 70% by mass to 90% by mass, based on 100% by mass of solution (B). When the concentration of the tetraalkoxysilane in solution (B) is 60% by mass or more, the reaction solution tends to become homogeneous. Furthermore, when the concentration of the tetraalkoxysilane in solution (B) is 95% by mass or less, the formation of a gel-like substance can be suppressed.

[0028] The concentration of the solvent in solution (B) is preferably 5% by mass to 40% by mass, more preferably 10% by mass to 30% by mass, based on 100% by mass of solution (B). When the concentration of the solvent in solution (B) is 5% by mass or more, the formation of a gel-like substance can be suppressed. Furthermore, when the concentration of the solvent in solution (B) is 40% by mass or less, the reaction solution tends to become homogeneous.

[0029] The addition rate of solution (B) per hour relative to the volume of solution (A) is preferably 0.05 kg / hour / L to 1.3 kg / hour / L, and more preferably 0.1 kg / hour / L to 0.8 kg / hour / L. When the addition rate of solution (B) is 0.05 kg / hour / L or more, excellent productivity of silica particles is achieved. Furthermore, when the addition rate of solution (B) is 1.3 kg / hour / L or less, the formation of a gel-like substance can be suppressed.

[0030] The solution (C) contains an alkali catalyst. Examples of alkali catalysts in solution (C) include ethylenediamine, diethylenetriamine, triethylenetetraamine, ammonia, urea, ethanolamine, and tetramethylammonium hydroxide. These alkali catalysts may be used alone or in combination of two or more. Among these alkali catalysts, ammonia is preferred because it has excellent catalytic activity, is easy to control particle shape, can suppress the inclusion of metal impurities, is highly volatile, and is easily removable after the hydrolysis reaction and the condensation reaction.

[0031] The solution (C) preferably contains a solvent, since this can reduce fluctuations in the concentration of the alkali catalyst in the reaction liquid. Examples of the solvent in solution (C) include water, methanol, ethanol, propanol, isopropanol, ethylene glycol, etc. These solvents may be used alone or in combination of two or more. Among these solvents, water and alcohol are preferred, and water is more preferred, because the solvents used in the hydrolysis reaction and the condensation reaction and the by-products are the same, and they are convenient for production.

[0032] The concentration of the alkali catalyst in solution (C) is preferably 0.5% by mass to 10% by mass, more preferably 1% by mass to 6% by mass, based on 100% by mass of solution (C). When the concentration of the alkali catalyst in solution (C) is 0.5% by mass or more, it is easy to adjust the concentration of the alkali catalyst in the reaction solution from the start to the end of the reaction. Furthermore, when the concentration of the alkali catalyst in solution (C) is 10% by mass or less, fluctuations in the concentration of the alkali catalyst in the reaction solution can be reduced.

[0033] The concentration of the solvent in solution (C) is preferably 90% by mass to 99.5% by mass, more preferably 94% by mass to 99% by mass, based on 100% by mass of solution (C). When the concentration of the solvent in solution (C) is 90% by mass or more, fluctuations in the concentration of the alkali catalyst in the reaction solution can be reduced. Furthermore, when the concentration of the solvent in solution (C) is 99.5% by mass or less, the concentration of the alkali catalyst in the reaction solution can be easily adjusted from the start to the end of the reaction.

[0034] The addition rate of solution (C) per hour relative to the volume of solution (A) is preferably 0.02 kg / hour / L to 0.5 kg / hour / L, and more preferably 0.04 kg / hour / L to 0.3 kg / hour / L. When the addition rate of solution (C) is 0.02 kg / hour / L or more, excellent productivity of silica particles is achieved. Furthermore, when the addition rate of solution (C) is 0.5 kg / hour / L or less, the formation of a gel-like substance can be suppressed.

[0035] Solutions (B) and (C) are added into solution (A). When using a highly volatile alkaline catalyst such as ammonia and when conducting hydrolysis and condensation reactions at high reaction temperatures, adding solutions (B) and (C) into solution (A) improves the miscibility of the components in the reaction solution, suppressing abnormal reactions in the air, and making it easier to control the circularity coefficient and particle size. "Adding into the solution" means adding below the liquid level; by positioning the supply outlet for solution (B) and the supply outlet for solution (C) below the liquid level of solution (A), solutions (B) and (C) can be added into solution (A).

[0036] The timing of adding solution (B) and solution (C) may be the same or may be different, such as alternately, but it is preferable that they are the same, as this reduces fluctuations in the reaction composition and makes the operation less complicated.

[0037] The reaction temperature for the hydrolysis reaction and condensation reaction is preferably 50°C to 80°C, more preferably 55°C to 75°C. When the reaction temperature is 50°C or higher, it becomes easy to control the particle shape such as the Heywood diameter and circularity coefficient. Furthermore, when the reaction temperature is 80°C or lower, bumping and solvent evaporation can be suppressed, and fluctuations in the reaction mixture can be reduced.

[0038] The water concentration in the reaction system for the hydrolysis and condensation reactions is preferably maintained at 3% to 30% by mass, and more preferably 5% to 25% by mass, based on the total amount (100% by mass) of the reaction system. When the water concentration in the reaction system is 3% by mass or more, it is easy to control the hydrolysis reaction rate of the tetraalkoxysilane. Furthermore, when the water concentration in the reaction system is 30% by mass or less, the reaction balance between the hydrolysis and condensation reactions is good, and it is easy to control the particle shape.

[0039] The concentration of the alkali catalyst in the reaction system for the hydrolysis reaction and condensation reaction is preferably maintained at 0.5% to 2.0% by mass, and more preferably at 0.6% to 1.5% by mass, based on the total amount (100% by mass) of the reaction system. When the concentration of the alkali catalyst in the reaction system is 0.5% by mass or more, aggregation of silica particles is suppressed, resulting in excellent dispersion stability of the silica particles in the dispersion. Furthermore, when the concentration of the alkali catalyst in the reaction system is 2.0% by mass or less, the reaction does not proceed excessively quickly, resulting in excellent reaction controllability.

[0040] The method for producing silica particles of the present invention preferably further comprises the following step (2) since it is possible to remove unnecessary components and add necessary components. Step (2): Concentrating the dispersion of silica particles obtained in step (1) and adding a dispersion medium

[0041] Examples of the dispersion medium include water, methanol, ethanol, propanol, isopropanol, and ethylene glycol. These dispersion media may be used alone or in combination of two or more. Among these dispersion media, water and alcohol are preferred, and water is more preferred, because they have excellent affinity with silica particles.

[0042] The method for producing silica particles of the present invention preferably further includes the following step (3) because the degree of condensation of silica particles can be increased. Step (3): A step of subjecting the dispersion of silica particles obtained in step (2) to a pressure and heat treatment.

[0043] The pressure of the heat-pressure treatment is preferably 0.10 MPa to 2.3 MPa, and more preferably 0.14 MPa to 1.0 MPa. When the heat-pressure treatment pressure is 0.10 MPa or higher, the degree of condensation of the silica particles can be increased. When the heat-pressure treatment pressure is 2.3 MPa or lower, silica particles can be produced without significant changes in the average primary particle size, average secondary particle size, cv value, or association ratio, resulting in excellent dispersion stability of the silica sol. Pressurization can be achieved by heating the silica particle dispersion in a sealed state to a temperature above the boiling point of the dispersion medium. When the silica particle aqueous dispersion is heated to 100°C or higher in a sealed state, the pressure becomes the saturated water vapor pressure at that temperature.

[0044] The temperature for the pressure and heat treatment is preferably 100°C to 220°C, and more preferably 110°C to 180°C. When the temperature for the pressure and heat treatment is 100°C or higher, the degree of condensation of the silica particles can be increased. When the temperature for the pressure and heat treatment is 220°C or lower, silica particles can be produced without significant changes in the average primary particle size, average secondary particle size, cv value, or association ratio, and the dispersion stability of the silica sol is excellent.

[0045] The time for the pressure and heat treatment is preferably 0.25 to 10 hours, more preferably 0.5 to 8 hours. When the time for the pressure and heat treatment is 0.25 hours or more, the degree of condensation of the silica particles can be increased. When the time for the pressure and heat treatment is 10 hours or less, silica particles can be produced without significant changes in the average primary particle size, average secondary particle size, cv value, and association ratio, and the dispersion stability of the silica sol is excellent.

[0046] The pressure and heat treatment is preferably carried out in an aqueous dispersion, since it can increase the degree of condensation of silica particles without significantly changing the average primary particle size, average secondary particle size, cv value, or association ratio.

[0047] The pH when the pressure and heat treatment is carried out in the aqueous dispersion is preferably 6.0 to 8.0, more preferably 6.5 to 7.8. When the pressure and heat treatment is carried out in the aqueous dispersion at a pH of 6.0 or higher, gelation of the silica sol can be suppressed. Furthermore, when the pressure and heat treatment is carried out in the aqueous dispersion at a pH of 8.0 or lower, the degree of condensation of the silica particles can be increased without significantly changing the average primary particle size, average secondary particle size, cv value, or association ratio.

[0048] (Physical properties of silica particles) The average Heywood diameter of the silica particles is preferably 30 nm or less, more preferably 5 nm to 25 nm, and even more preferably 6 nm to 20 nm. When the average Heywood diameter of the silica particles is 5 nm or more, the storage stability of the silica sol is excellent. Furthermore, when the average Heywood diameter of the silica particles is 30 nm or less, when the silica particles are used as a polishing composition, a polished object having a smooth surface can be obtained, and the polishing performance can be stabilized.

[0049] The standard deviation of the Heywood diameter of the silica particles is preferably 0.10 nm to 4.00 nm, more preferably 0.50 nm to 3.00 nm. When the standard deviation of the Heywood diameter of the silica particles is 0.10 nm or more, the silica particles can be easily produced. Furthermore, when the standard deviation of the Heywood diameter of the silica particles is 4.00 nm or less, secondary aggregation of the silica particles is suppressed, and the dispersion stability of the silica particles in the dispersion is excellent. When the silica particles are used as a polishing composition, a polished object with a smooth surface can be obtained, and the polishing performance stability is excellent.

[0050] The average major axis of the silica particles is preferably 32 nm or less, more preferably 6 nm to 27 nm, and even more preferably 7 nm to 22 nm. When the average major axis of the silica particles is 6 nm or more, the storage stability of the silica sol is excellent. Furthermore, when the average major axis of the silica particles is 32 nm or less, when the silica particles are used as a polishing composition, a polished object having a smooth surface is obtained, and the polishing performance is stable.

[0051] The average minor axis of the silica particles is preferably 28 nm or less, more preferably 4 nm to 23 nm, and even more preferably 5 nm to 18 nm. When the average minor axis of the silica particles is 4 nm or more, the storage stability of the silica sol is excellent. Furthermore, when the average minor axis of the silica particles is 28 nm or less, when the silica particles are used as a polishing composition, a polished object having a smooth surface is obtained, and the polishing performance is stable.

[0052] The average circularity coefficient of the silica particles is preferably 0.87 to 0.99, more preferably 0.90 to 0.98. When the average circularity coefficient of the silica particles is 0.87 or more, secondary aggregation of the silica particles is suppressed, and the dispersion stability of the silica particles in a dispersion is excellent. When the silica particles are used as a polishing composition, a polished object having a smooth surface is obtained, and the polishing performance is excellent in stability. Furthermore, when the average circularity coefficient of the silica particles is 0.99 or less, the silica particles can be easily produced.

[0053] The standard deviation of the circularity coefficient of the silica particles is preferably 0.01 to 0.08, more preferably 0.02 to 0.05. When the standard deviation of the circularity coefficient of the silica particles is 0.01 or more, the silica particles can be easily produced. Furthermore, when the standard deviation of the circularity coefficient of the silica particles is 0.08 or less, secondary aggregation is suppressed and dispersion stability is excellent. When the silica particles are used as a polishing composition, a polished object having a smooth surface can be obtained, and the polishing performance stability is excellent.

[0054] The average aspect ratio of the silica particles is preferably 1.01 to 1.30, more preferably 1.02 to 1.20. When the average aspect ratio of the silica particles is 1.01 or more, the silica particles can be easily produced. When the average aspect ratio of the silica particles is 1.30 or less, secondary aggregation of the silica particles is suppressed, and the dispersion stability of the silica particles in the dispersion is excellent. When the silica particles are used as a polishing composition, a polished object having a smooth surface can be obtained, and the polishing performance can be stable.

[0055] The standard deviation of the aspect ratio of the silica particles is preferably 0.01 to 0.20, more preferably 0.02 to 0.15. When the standard deviation of the aspect ratio of the silica particles is 0.01 or more, the silica particles can be easily produced. Furthermore, when the standard deviation of the aspect ratio of the silica particles is 0.20 or less, secondary aggregation of the silica particles is suppressed, and the dispersion stability of the silica particles in the dispersion is excellent. When the silica particles are used as a polishing composition, a polished object having a smooth surface can be obtained, and the polishing performance can be stable.

[0056] The average values ​​and standard deviations of the circularity coefficient, Heywood diameter, major axis, minor axis, and aspect ratio of the silica particles are measured using a field emission scanning electron microscope. Specifically, the measurements and calculations are performed under the following conditions.

[0057] A dispersion of silica particles is dropped onto a silicon substrate and dried. The silicon substrate is then irradiated with an electron beam at an accelerating voltage of 5 kV using a field-emission scanning electron microscope. Secondary electron images are then taken at a magnification of 50,000 to 200,000 times to ensure that the total number of silica particles is 80 or more. The Heywood diameter, major axis, minor axis, circularity coefficient, and aspect ratio of all silica particles are measured, and their average values ​​and standard deviations are calculated. The concentration of silica particles in the dispersion may be adjusted as needed.

[0058] The shape of silica particles is determined as described below. Whether two or more silica particles are bonded together is determined as follows: if black lines are visible between the silica particles, they are determined to be individual silica particles that are not bonded together; if no black lines are visible between the silica particles, they are determined to be a single bonded silica particle. Furthermore, if three or more silica particles are aggregated together, it is difficult to determine, so they are excluded from the measurement.

[0059] The reason why the magnification of the field emission scanning electron microscope was set to 50,000 to 200,000 times was to enable identification of the shape of each silica particle of 30 nm or less.

[0060] The circularity coefficient is 4πS / L, where S is the area of ​​the secondary electron image of a silica particle photographed with the above-mentioned field emission scanning electron microscope, and L is the perimeter of the secondary electron image. 2 The value is calculated as follows. The Heywood diameter is the diameter of a circle that has the same area as the secondary electron image. The major axis is the long side of a rectangle that circumscribes the secondary electron image and has the smallest area. The minor axis is the short side of a rectangle that circumscribes the secondary electron image and has the smallest area. The aspect ratio is defined as the long side of the rectangle that circumscribes the secondary electron image with the smallest area, D L The short side of the rectangle that circumscribes the secondary electron image and has the smallest area is DS When L / D S The value is calculated as follows.

[0061] The content of metal impurities in the silica particles is preferably 5 ppm or less, more preferably 2 ppm or less.

[0062] When polishing silicon wafers for semiconductor devices, metallic impurities adhere to and contaminate the surface of the workpiece, adversely affecting the wafer characteristics and diffusing into the wafer, degrading its quality, resulting in a significant decrease in the performance of semiconductor devices manufactured from such wafers. Furthermore, if metal impurities are present on silica particles, coordination interactions occur between the acidic surface silanol groups and the metal impurities, which changes the chemical properties (acidity, etc.) of the surface silanol groups and the three-dimensional environment of the silica particle surface (e.g., the ease of silica particle aggregation), thereby affecting the polishing rate.

[0063] The metal impurity content of silica particles is measured using inductively coupled plasma mass spectrometry (ICP-MS). Specifically, a silica sol containing 0.4 g of silica particles is accurately weighed, sulfuric acid and hydrofluoric acid are added, and the mixture is heated, dissolved, and evaporated. Pure water is added to the remaining sulfuric acid droplets to a total of exactly 10 g to create a test solution, which is then measured using an inductively coupled plasma mass spectrometer. The target metals are sodium, potassium, iron, aluminum, calcium, magnesium, zinc, cobalt, chromium, copper, manganese, lead, titanium, silver, and nickel, and the total content of these metals is the metal impurity content.

[0064] The metal impurity content of silica particles can be reduced to 5 ppm or less by obtaining silica particles through hydrolysis and condensation reactions using alkoxysilane as the main raw material. In the method of deionizing alkali silicate such as water glass, sodium and other impurities derived from the raw material remain, making it extremely difficult to reduce the metal impurity content of silica particles to 5 ppm or less.

[0065] Silica particles preferably do not have pores because they have excellent mechanical strength and storage stability. The presence or absence of pores in silica particles is confirmed by multipoint BET analysis using adsorption isotherms with nitrogen as the adsorption gas.

[0066] (Method of producing silica sol) The method for producing a silica sol of the present invention includes the method for producing silica particles of the present invention.

[0067] The silica sol may be produced by using the dispersion of silica particles obtained by the method for producing silica particles of the present invention as is, or by removing unnecessary components from the dispersion of silica particles obtained and adding necessary components.

[0068] The silica sol preferably contains silica particles and a dispersion medium. Examples of the dispersion medium in the silica sol include water, methanol, ethanol, propanol, isopropanol, and ethylene glycol. These dispersion media in the silica sol may be used alone or in combination of two or more. Among these dispersion media in the silica sol, water and alcohol are preferred, and water is more preferred, because they have excellent affinity with silica particles.

[0069] The content of silica particles in the silica sol is preferably 3% by mass to 50% by mass, more preferably 4% by mass to 40% by mass, and even more preferably 5% by mass to 30% by mass, based on 100% by mass of the total amount of silica sol. When the content of silica particles in the silica sol is 3% by mass or more, the polishing rate for a workpiece such as a silicon wafer is excellent. Furthermore, when the content of silica particles in the silica sol is 50% by mass or less, aggregation of silica particles in the silica sol or polishing composition can be suppressed, and the storage stability of the silica sol or polishing composition is excellent.

[0070] The content of the dispersion medium in the silica sol is preferably 50% by mass to 97% by mass, more preferably 60% by mass to 96% by mass, and even more preferably 70% by mass to 95% by mass, based on the total amount of the silica sol (100% by mass). When the content of the dispersion medium in the silica sol is 50% by mass or more, aggregation of silica particles in the silica sol or polishing composition can be suppressed, resulting in excellent storage stability of the silica sol or polishing composition. Furthermore, when the content of the dispersion medium in the silica sol is 97% by mass or less, the polishing rate for a workpiece, typically a silicon wafer, is excellent.

[0071] The content of silica particles and dispersion medium in the silica sol can be set within a desired range by removing unnecessary components from the components in the obtained dispersion of silica particles and adding necessary components.

[0072] In addition to silica particles and a dispersion medium, the silica sol may contain other components such as an oxidizing agent, an antiseptic, an antifungal agent, a pH adjuster, a pH buffer, a surfactant, a chelating agent, and an antibacterial / biocide, as needed, within a range that does not impair the performance of the silica sol. In particular, it is preferable to include an antibacterial biocide in the silica sol, since this gives the silica sol excellent storage stability.

[0073] Examples of antibacterial biocides include hydrogen peroxide, ammonia, quaternary ammonium hydroxides, quaternary ammonium salts, ethylenediamine, glutaraldehyde, hydrogen peroxide, methyl p-hydroxybenzoate, and sodium chlorite. These antibacterial biocides may be used alone or in combination of two or more. Among these antibacterial biocides, hydrogen peroxide is preferred because of its excellent affinity with silica sol. Biocides also include those commonly referred to as fungicides.

[0074] The content of the antibacterial biocide in the silica sol is preferably 0.0001% by mass to 10% by mass, and more preferably 0.001% by mass to 1% by mass, based on the total amount of the silica sol (100% by mass). When the content of the antibacterial biocide in the silica sol is 0.0001% by mass or more, the storage stability of the silica sol is excellent. When the content of the antibacterial biocide in the silica sol is 10% by mass or less, the original performance of the silica sol is not impaired.

[0075] The pH of the silica sol is preferably 6.0 to 8.0, more preferably 6.5 to 7.8. When the pH of the silica sol is 6.0 or higher, the dispersion stability is excellent and aggregation of the silica particles can be suppressed. Furthermore, when the pH of the silica sol is 8.0 or lower, dissolution of the silica particles is prevented and long-term storage stability is excellent. The pH of the silica sol can be adjusted to a desired range by adding a pH adjuster.

[0076] (polishing composition) The silica sol obtained by the method for producing a silica sol of the present invention can be suitably used as a polishing composition. The polishing composition preferably contains the above-mentioned silica sol and water-soluble polymer.

[0077] The water-soluble polymer enhances the wettability of the polishing composition to the object to be polished, such as a silicon wafer. The water-soluble polymer is preferably a polymer having a functional group with high water affinity, and this functional group with high water affinity has a high affinity with the surface silanol groups of the silica particles, so that the silica particles and the water-soluble polymer are stably dispersed in close proximity in the polishing composition. Therefore, when polishing an object to be polished, such as a silicon wafer, the effects of the silica particles and the water-soluble polymer function synergistically.

[0078] Examples of water-soluble polymers include cellulose derivatives, polyvinyl alcohol, polyvinylpyrrolidone, copolymers having a polyvinylpyrrolidone skeleton, and polymers having a polyoxyalkylene structure.

[0079] Examples of cellulose derivatives include hydroxyethyl cellulose, hydrolyzed hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, ethyl cellulose, ethyl hydroxyethyl cellulose, and carboxymethyl cellulose. Examples of copolymers having a polyvinylpyrrolidone skeleton include graft copolymers of polyvinyl alcohol and polyvinylpyrrolidone. Examples of polymers having a polyoxyalkylene structure include polyoxyethylene, polyoxypropylene, and copolymers of ethylene oxide and propylene oxide.

[0080] These water-soluble polymers may be used alone or in combination of two or more. Among these water-soluble polymers, cellulose derivatives are preferred, and hydroxyethyl cellulose is more preferred, because they have high affinity with the surface silanol groups of silica particles and act synergistically to impart good hydrophilicity to the surface of the object to be polished.

[0081] The mass-average molecular weight of the water-soluble polymer is preferably 1,000 to 3,000,000, more preferably 5,000 to 2,000,000, and even more preferably 10,000 to 1,000,000. When the mass-average molecular weight of the water-soluble polymer is 1,000 or more, the hydrophilicity of the polishing composition is improved. Furthermore, when the mass-average molecular weight of the water-soluble polymer is 3,000,000 or less, the affinity with silica sol is excellent and the polishing rate for a workpiece, such as a silicon wafer, is excellent.

[0082] The mass average molecular weight of the water-soluble polymer is measured by size exclusion chromatography using a 0.1 mol / L NaCl solution as the mobile phase, in terms of polyethylene oxide.

[0083] The content of the water-soluble polymer in the polishing composition is preferably 0.02% by mass to 10% by mass, more preferably 0.05% by mass to 5% by mass, based on 100% by mass of the total amount of the polishing composition. When the content of the water-soluble polymer in the polishing composition is 0.02% by mass or more, the hydrophilicity of the polishing composition is improved. Furthermore, when the content of the water-soluble polymer in the polishing composition is 10% by mass or less, aggregation of silica particles during preparation of the polishing composition can be suppressed.

[0084] In addition to the silica sol and the water-soluble polymer, the polishing composition may contain other components, such as basic compounds, polishing accelerators, surfactants, hydrophilic compounds, preservatives, antifungal agents, pH adjusters, pH buffers, surfactants, chelating agents, and antibacterial and biocide agents, as needed, provided that the performance of the polishing composition is not impaired. In particular, it is preferable to include a basic compound in the polishing composition, since it can exert a chemical action on the surface of the object to be polished, such as a silicon wafer, thereby performing chemical polishing (chemical etching), and the synergistic effect with the surface silanol groups of the silica particles can improve the polishing rate of the object to be polished, such as a silicon wafer.

[0085] Examples of basic compounds include organic basic compounds, alkali metal hydroxides, alkali metal hydrogencarbonates, alkali metal carbonates, and ammonia. These basic compounds may be used alone or in combination of two or more. Among these basic compounds, ammonia, tetramethylammonium hydroxide, tetraethylammonium hydroxide, ammonium hydrogencarbonate, and ammonium carbonate are preferred because they have high water solubility and excellent affinity with silica particles and water-soluble polymers, with ammonia, tetramethylammonium hydroxide, and tetraethylammonium hydroxide being more preferred, and ammonia being even more preferred.

[0086] The content of the basic compound in the polishing composition is preferably 0.001% by mass to 5% by mass, more preferably 0.01% by mass to 3% by mass, based on 100% by mass of the total amount of the polishing composition. When the content of the basic compound in the polishing composition is 0.001% by mass or more, the polishing rate of a polished object, typically a silicon wafer, can be improved. Furthermore, when the content of the basic compound in the polishing composition is 5% by mass or less, the stability of the polishing composition is excellent.

[0087] The pH of the polishing composition is preferably 8.0 to 12.0, more preferably 9.0 to 11.0. When the pH of the polishing composition is 8.0 or higher, aggregation of silica particles in the polishing composition can be suppressed, and the polishing composition has excellent dispersion stability. When the pH of the polishing composition is 12.0 or lower, dissolution of silica particles can be suppressed, and the polishing composition has excellent stability. The pH of the polishing composition can be adjusted to a desired range by adding a pH adjuster.

[0088] The polishing composition can be obtained by mixing the silica sol obtained by the silica sol manufacturing method of the present invention, the water-soluble polymer, and, if necessary, other components. However, in consideration of storage and transportation, the polishing composition can be prepared at a high concentration first and then diluted with water or the like immediately before polishing.

[0089] (polishing method) The polishing method of the present invention is a polishing method using a polishing composition containing the silica sol obtained by the method for producing silica sol of the present invention. The polishing composition used is preferably the polishing composition described above. A specific polishing method includes, for example, a method in which the surface of a silicon wafer is pressed against a polishing pad, the polishing composition of the present invention is dropped onto the polishing pad, and the surface of the silicon wafer is polished.

[0090] (Semiconductor wafer manufacturing method) The method for producing a semiconductor wafer of the present invention includes the polishing method of the present invention, and the specific polishing method is as described above. Examples of semiconductor wafers include silicon wafers and compound semiconductor wafers.

[0091] (Semiconductor device manufacturing method) The method for manufacturing a semiconductor device of the present invention includes the polishing method of the present invention, and the specific polishing method is as described above.

[0092] (Application) The silica particles obtained by the method for producing silica particles of the present invention and the silica sol obtained by the method for producing silica sol of the present invention can be suitably used for polishing purposes, such as polishing semiconductor materials such as silicon wafers, polishing electronic materials such as hard disk substrates, polishing (chemical mechanical polishing) in the planarization process when producing integrated circuits, polishing synthetic quartz glass substrates used for photomasks and liquid crystal displays, and polishing magnetic disk substrates, and among these, they can be particularly suitably used for polishing silicon wafers and chemical mechanical polishing.

[0093] The silica particles obtained by the method for producing silica particles of the present invention are silica particles with a large circularity coefficient and a small particle diameter, so when used as a composite material with resins, they impart transparency and water repellency to the resins, and also improve dispersibility and mixability, thereby improving the processability of the composite material.Therefore, the silica particles obtained by the method for producing silica particles of the present invention can also be suitably used as a hard coating agent, a paint, or a ceramic binder. [Example]

[0094] The present invention will be explained in more detail below using examples, but the present invention is not limited to the description of the following examples as long as it does not deviate from the gist of the invention.

[0095] (Measurement of silica particle shape) The silica particle dispersions obtained in the examples and comparative examples were diluted 5,000 times with ultrapure water, and 5 μL of the diluted silica particle dispersion was dropped onto a silicon substrate and dried. Next, using a field emission scanning electron microscope (model "S-5200" manufactured by Hitachi High-Technologies Corporation, FE-SEM), the silicon substrate was irradiated with an electron beam at an accelerating voltage of 5 kV, and secondary electron images were taken at magnifications of 50,000 to 200,000 to ensure that the total number of silica particles was 80 or more. The Heywood diameter, major axis, minor axis, circularity coefficient, and aspect ratio of all silica particles were measured, and the average value and standard deviation were also measured. The shape of the silica particles was measured by importing the field emission scanning electron microscope photographs into image analysis particle size distribution measurement software (software name "Mac-View Ver. 4", manufactured by Mountec Co., Ltd.). The shape of silica particles was determined as described below. Whether two or more silica particles were bonded together was determined as follows: if black lines were visible between the silica particles, they were determined to be individual silica particles that were not bonded together; if no black lines were visible between the silica particles, they were determined to be a single silica particle that was bonded together. Furthermore, if three or more silica particles were aggregated together, it was difficult to determine the aggregated silica particles, so they were excluded from the measurement.

[0096] [Example 1] Solution (B) of 100 parts by mass of tetramethoxysilane and 33.3 parts by mass of methanol and solution (C) of 25.0 parts by mass of pure water and 2.2 parts by mass of 29% by mass of ammonia water were added to solution (A) of 34.2 parts by mass of pure water, 188.3 parts by mass of methanol, and 8.8 parts by mass of 29% by mass of ammonia water at a constant rate over 103 minutes. During the addition, the reaction solution was stirred while maintaining the temperature at 70°C. After the addition was completed, the reaction solution was stirred for an additional 30 minutes while maintaining the temperature at 70°C. The temperature of the obtained dispersion of silica particles was raised to remove methanol and ammonia while adjusting the liquid volume by adding pure water so that the silica particle content was approximately 20% by mass, thereby obtaining a dispersion of silica particles with a silica particle content of approximately 20% by mass. The evaluation results of the obtained silica particles are shown in Table 1.

[0097] [Example 2] The same procedure as in Example 1 was carried out except that the reaction temperature and the holding temperature were set to 60°C, to obtain a dispersion of silica particles with a silica particle content of about 20 mass %. The evaluation results of the obtained silica particles are shown in Table 1.

[0098] [Example 3] Solution (B) of 100 parts by mass of tetramethoxysilane and 17.6 parts by mass of methanol and solution (C) of 21.5 parts by mass of pure water and 2.1 parts by mass of 29% by mass of ammonia water were added to solution (A) of 40.6 parts by mass of pure water, 207.6 parts by mass of methanol, and 5.2 parts by mass of 29% by mass of ammonia water at a constant rate over 93 minutes. During the addition, the reaction solution was stirred while maintaining the temperature at 50°C. After the addition was completed, the reaction solution was stirred for an additional 30 minutes while maintaining the temperature at 50°C. The temperature of the obtained dispersion of silica particles was raised to remove methanol and ammonia while adjusting the liquid volume by adding pure water so that the silica particle content was approximately 20% by mass, thereby obtaining a dispersion of silica particles with a silica particle content of approximately 20% by mass. The evaluation results of the obtained silica particles are shown in Table 1.

[0099] [Example 4] Solution (B) of 100 parts by mass of tetramethoxysilane and 17.6 parts by mass of methanol and solution (C) of 19.4 parts by mass of pure water and 5.3 parts by mass of 29% by mass of ammonia water were added to solution (A) of 34.9 parts by mass of pure water, 204.4 parts by mass of methanol, and 13.1 parts by mass of 29% by mass of ammonia water at a constant rate over 94 minutes. During the addition, the reaction solution was stirred while maintaining the temperature at 70°C. After the addition was completed, the reaction solution was stirred for an additional 30 minutes while maintaining the temperature at 70°C. The temperature of the obtained dispersion of silica particles was raised to remove methanol and ammonia while adjusting the liquid volume by adding pure water so that the silica particle content was approximately 20% by mass, thereby obtaining a dispersion of silica particles with a silica particle content of approximately 20% by mass. The evaluation results of the obtained silica particles are shown in Table 1.

[0100] [Comparative Example 1] The same operation as in Example 1 was carried out, except that solution (B) and solution (C) were added dropwise from above the liquid surface of solution (A) rather than into the liquid of solution (A). However, a large amount of silica particles adhered to the inner wall of the reaction vessel, the stirring blades, etc., making it difficult to continue the operation thereafter.

[0101] [Table 1]

[0102] As can be seen from Table 1, the silica particles obtained by the manufacturing methods of Examples 1 to 4 have a large average circularity coefficient, small average Heywood diameters, small average major diameters, small average minor diameters, and small average aspect ratios, and their standard deviations are also small, indicating that the silica particles have small particle shape variation and particle diameters. The silica particles obtained in Examples 1 to 4 have small particle shape variations and particle diameters, and therefore, when used as a polishing composition, it is expected that a polished object with a smooth surface will be obtained and that the polishing performance will be stable. Furthermore, the dispersion of silica particles obtained in Example 1 was similarly evaluated 9 months after production, and it showed almost no change, and secondary aggregation was not observed at all, indicating excellent dispersion stability. [Industrial Applicability]

[0103] The silica particles obtained by the method for producing silica particles of the present invention and the silica sol obtained by the method for producing silica sol of the present invention can be suitably used for polishing purposes, such as polishing semiconductor materials such as silicon wafers, polishing electronic materials such as hard disk substrates, polishing (chemical mechanical polishing) in the planarization process when producing integrated circuits, polishing synthetic quartz glass substrates used for photomasks and liquid crystal displays, and polishing magnetic disk substrates, and among these, they can be particularly suitably used for polishing silicon wafers and chemical mechanical polishing.

Claims

1. A method for producing silica particles, comprising the following step (1): Step (1): A step of adding a solution (B) containing a tetraalkoxysilane and a solution (C) containing an alkali catalyst to a solution (A) containing an alkali catalyst, and causing the tetraalkoxysilane to undergo a hydrolysis reaction and a condensation reaction.

2. The method for producing silica particles according to claim 1 , wherein the alkali catalyst in the solution (A) is ammonia.

3. The method for producing silica particles according to claim 1 or 2, wherein the alkali catalyst in the solution (C) is ammonia.

4. The method for producing silica particles according to any one of claims 1 to 3, wherein the reaction temperatures of the hydrolysis reaction and the condensation reaction are 50°C or higher.

5. 5. The method for producing silica particles according to claim 1, wherein the average Heywood diameter of the silica particles measured by a field emission scanning electron microscope is 20 nm or less.

6. The method for producing silica particles according to any one of claims 1 to 5, further comprising the following step (2): Step (2): Concentrating the dispersion of silica particles obtained in step (1) and adding a dispersion medium

7. The method for producing silica particles according to claim 6, further comprising the following step (3): Step (3): A step of subjecting the dispersion of silica particles obtained in step (2) to a pressure and heat treatment.

8. A method for producing a silica sol, comprising the method for producing silica particles according to any one of claims 1 to 7.

9. The method for producing a silica sol according to claim 8, wherein the concentration of silica particles in the silica sol is 3% by mass to 50% by mass.

10. A polishing method, comprising polishing using a polishing composition containing the silica sol obtained by the method for producing a silica sol according to claim 8 or 9.

11. A method for manufacturing a semiconductor wafer, comprising the polishing method according to claim 10.

12. A method for manufacturing a semiconductor device, comprising the polishing method according to claim 10.

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